mmm, there can't be a cannonical source for message types @cinnamon - this is the subjective web remember. Having said that, I think a good pattern would be for people to publish clearly the schemas they're using ... somewhere. I made a start by adding to this repo https://github.com/ssbc/ssb-msg-schemas - it has validators which check whether a message has the parts needed for whatever you're writing to be able to uses it.